JPH08293703A - Cavity type band-pass filter with comb line structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate or reduce the restriction on the high-frequency section of the passing band of a band-pass filter without adding any stopping band-pass filter in series to the objective band-pass filter by adding one or a plurality of resonance circuits which appropriately select tuning frequencies by themselves to the filter at one or a plurality of appropriate points in the filter pack. SOLUTION: Four rejectors R1e, R2e, R1s, and R2s are arranged closely to the input and output terminals of a filter. Namely, the rejectors R1e and R2e are respectively arranged between an input bar Be and the end section of a waveguide provided closely to the bar Be and between the bar Be and a resonance circuit B1-V1. The rejectors R2s and R1s are respectively arranged between a resonance circuit B3-V3 and an output bar Bs and between the output bar Bs and the end section of a waveguide provided closely to the bar Bs. Since the rejectors R2e and R2s are arranged perpendicularly to the resonance circuits B1-V1 and B3-V3 themselves of the filter adjacently to the ports of the filter, the passing band of the filter is not disturbed so much.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cavity bandpass filter having a combline structure, and more particularly to a cavity bandpass filter used as an input filter of a radio receiver.

[0002]

2. Description of the Related Art A wireless altimeter equipped with a cavity type combline structure bandpass filter is commercially available. The filters used have very low insertion loss and no spurious passband near the effective passband. On the other hand, the flank of the pass band is the flank of a Chebyshev filter and is gentle. This causes problems, especially for flanks, in some applications, limiting the high frequency portion of the passband.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate or at least reduce the above problems without adding a stop band filter in series with a target band filter.

[0004]

The above objective is to add one or more resonant circuits whose tuning frequency is properly selected per se to the filter at the appropriate one or more points in the filter pack. Can be achieved by doing.

According to the present invention, a cavity type bandpass filter having a center frequency Fo having a comb line structure can be obtained. The filter comprises a parallelepiped pack, the parallelepiped pack having a first end, a second end, two first inner walls parallel to each other, and parallel to each other perpendicular to the first inner wall. Two second inner walls and a first end, a first section, a first port of the filter, a second section, a continuous comb tooth, a third section, a second port of the filter, a fourth And a continuous assembly in which the second ends are lined up in series,
Each of the ports and each of the comb teeth has a bar attached perpendicular to the first inner wall, and n is an integer of 0 <n <5, and n sections of the four sections are respectively A rejector mounted perpendicular to the second inner wall
or)).

The following description and the accompanying drawings will provide a better understanding of the present invention and other features.

1 to 4, corresponding elements are designated by the same reference numerals.

[0008]

1 and 2 are a longitudinal sectional view and a bottom view of a conventional cavity bandpass filter having a three-tooth comb line structure with a cover removed. 2, the cross section along FIG. 1 is the axis corresponding to the projection by the two arrows XX of the cross section lying in the plane of FIG. 2 out of the two cross sections shown in FIG. Have been identified.

The filter of FIGS. 1 and 2 comprises a hollow component 1
And a metal parallelepiped pack with a lid 2.

Two metal bars Be and Bs are fixedly joined to the bottom of the hollow component and arranged perpendicular to the bottom. Three metal tuning screws V1, V2, V3
Has its head outside the pack, but penetrates the bottom of the hollow part vertically from one side to the other and penetrates into the pack at different depths. Bar Be, screws V1, V
2, V3, and the bar Bs are aligned in this order.

The two metal connectors Pe, Ps and the bars B1, B2, B3 are fixedly joined to the lid 2. The connector is located in the extension of the hole provided in the lid and has three bars B1, B forming the three teeth of the comb.
2 and B3 are vertically attached to the lid. Coaxial cables Le and Ls, of which only the ends are shown, penetrate the connectors Pe and Ps, respectively, and their internal conductors are insulated from the lid by an insulator protruding from the lid on the side opposite to the connectors. The outer conductor of the coaxial cable is in contact with the inner wall of the connector. In FIG. 2, when the lid 1 is placed on the hollow portion 2 as shown in FIG.
The positions of the inner conductor of s and the bars B1, B2, B3 in the pack are indicated by broken lines. As shown in FIGS. 1 and 2, the cables Le, Ls form the input and output conductors of the filter.

The bars B1, B2, B3 form a wave rejector,
Screws V located in front of the bars B1, B2, B3 respectively
1, V2, V3 form the tuning element of the resonant frequency of the resonant circuit. The filter as shown in FIGS. 1 and 2 is considered to be a three-cavity filter, and the spaces adjacent to each of the bars B1, B2, B3 are hollow.

In the exemplary embodiments described herein,
Pack 1, lid 2 and bars Be, B1, B2, B
3 and Bs are made of light alloy, and the inner wall of the waveguide formed by the pack and the lid is plated with chrome. The tuning screws V1, V2, V3 are made of beryllium bronze.

The dimensions of the pack of filters according to FIGS. 1 and 2 are as follows.

External dimensions: length 60 mm, width 17 mm of side surface parallel to plane of FIG. 1, width 1 of side surface parallel to plane of FIG.
8 mm-Internal dimensions: length 55 mm, width of wall parallel to plane of FIG. 1 10 mm, width of wall parallel to plane of FIG. 2 12 mm This bandpass filter has an amplitude response A with respect to frequency F at a curve Ch of FIG. It is represented and is centered around 4.3 GHz. The curve Ch is a standard curve of the Chebyshev filter. This type of filter has low insertion loss and has no spurious passband in the cutoff band. In contrast to this,
The slope of the transition between the pass band and the cut-off band is extremely small, especially compared to the Cauer filter. However, it is not known how to fabricate a Cauer filter with a mechanical structure, i.e. in the form of a comb-lined hollow filter. However, it is possible to manufacture the Cauer filter by other techniques, such as the microstrip technique. The disadvantage in that case is that in such an embodiment spurious passbands appear in the cutoff band.

FIGS. 3 and 4 show four filters R1e, R2e, R1s and R2 in the filter according to FIGS.
It is a figure which shows the pass band filter which can add s,
In the above example, the wave rejector is made of beryllium bronze.
In the above figure, it is necessary to show the position where the wave remover can be arranged so as to improve the response of the filter. In this example, it is only necessary to implement the wave removers R2e, R2s to achieve the required improvement. In other applications, only one wave remover may be sufficient, or three or all four wave removers may have to be used.

These four wave removers are arranged close to the input terminal and the output terminal of the filter. That is, R1
e is between the input bar Be and the end of the waveguide adjacent to this bar, R2e is between the input bar Be and the resonance circuit B1-V1, and R2s is the resonance circuit B3-V3 and the output bar Bs. , R1s is placed between the output bar Bs and the end of the waveguide adjacent to it.

The four wave removers are mounted vertically on the inner wall of the pack, particularly on the wall parallel to the plane of FIG. That is, it is mounted vertically to the resonance circuit of the filter.

The advantage of arranging the demultiplexer adjacent to the port of the filter and perpendicularly to the resonant circuit of the filter is that the demultiplexer performs the original function of the demultiplexer. As can be seen from 5, the wave remover extracts energy at its tuning frequency without significantly disturbing the pass band of the filter.

FIG. 5 corresponds to the illustrative filter, ie, the filter according to FIGS. 3 and 4 as described above, but with the curve Ch representing the amplitude / frequency response of the filter according to FIGS. 1 and 2. 3 shows a curve Ci representing the magnitude / frequency response of a filter without the resistors R1e and R1s.

By comparing the curves Ci and Ch, it can be seen that the filter characteristics in the high frequency part of the pass band of the filter can be improved by about 30 decibels by introducing the wave removers R2e and R2s into the filter shown in FIGS. . The pass band according to the curve Ci is centered at Fo = 4.3 GHz and when compared to the pass band according to the curve Ch, it decreases slightly at the top of the band and broadens slightly at the bottom of the band.

In the example described above, the demultiplexers R2e and R2s
At resonance frequencies of about 4.5 GHz and 4.6 G, respectively.
It is tuned to Hz. Therefore, the curve Ci has a valley at the above frequency. This trough is due to the resonant circuit extracting energy at its tuning frequency.
It should be noted that the two wave removers are tuned to a tuning frequency higher than the frequency of the pass band of the filter. The reason is that the wave remover operates normally only under this condition. At tuning frequencies lower than the filter passband, large spurious passbands appear in the response curve, which is generally undesirable.

The present invention is not limited to the above embodiments. That is, the number of teeth of the comb line structure can be other than three. The bars such as Be, Bs, etc., and the teeth of the comb may be perpendicular to the innermost wall of the waveguide in the longitudinal direction, but not to the innermost one of the inner walls. In this case, in order to keep the wave remover orthogonal to them, the wave remover is mounted perpendicular to the innermost wall of the waveguide in the longitudinal direction.

The application of the present invention is in particular wireless altimeters.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a filter according to the prior art.

FIG. 2 is a schematic diagram of a filter according to the prior art.

FIG. 3 is a schematic diagram of a filter according to the present invention.

FIG. 4 is a schematic diagram of a filter according to the present invention.

FIG. 5 is a graph associated with the filter according to FIGS. 1 to 4.

[Explanation of symbols]

 1 Cavity 2 Lid B1, B2, B3 Bar Be, Bs Bar Pe, Ps Connector V1, V2, V3 Screw Le, Ls Coaxial cable

Claims (3)

[Claims] 1. A parallelepiped pack comprising a first end portion, a second end portion, two first inner walls parallel to each other, and parallel to each other perpendicular to the first inner wall. Two second inner walls and a first end, a first section, a first port of the filter, a second section, a continuous comb tooth, a third section, a second port of the filter, Four sections and a continuous assembly in which the second ends are lined up in series,
Each of the ports and comb teeth has a bar attached perpendicularly to the first inner wall, and n is an integer of 0 <n <5, and n sections among the four sections are respectively Cavity bandpass filter with center frequency Fo having a combline structure, comprising a wave rejector mounted perpendicular to the second inner wall. 2. The bandpass filter according to claim 1, wherein at least one of the n wave cancellers has a tuning frequency higher than Fo. 3. The method according to claim 1, wherein n is equal to 2 and the two demultiplexers each have a tuning frequency higher than Fo and are located in the second and third sections, respectively. Bandpass filter as described.